The present invention relates generally to lead-acid storage batteries, and more particularly, to a method and apparatus for casting straps onto the plate lugs of battery cell elements.
Heretofore, it has been the practice to assemble battery cell elements comprising a plurality of lead grids coated or filled with suitable paste and grouped as alternative positive and negative plates separated by interleaved electrical insulating separators and then to secure and electrically couple the assembly of plates by casting straps of a lead or lead alloy onto respective groups of lugs for the positive and negative plates. While different approaches have been proposed for casting such lug straps, they have suffered from various drawbacks, including inefficient and slow operation and difficulties in controlling casting conditions.
Problems have been incurred, for example, in controlling the temperature of the mold and molten lead for optimum and efficient casting. In processes where hot molten lead is introduced into an unpreheated, relatively cool mold, although cooling of the molten lead is expedited, the timing in which the element lugs must be placed into the rapidly cooling molten lead is critical, and a delay of only a fraction of a second can affect the quality of the casting. To minimize such timing problems, others have proposed preheating the mold to substantially the temperature of the molten lead by passing heated fluids through passageways in the mold, or by incorporating electrical heating elements in the mold. Such approaches, however, increase the mass of the mold, which in turn makes heating and cooling of the mold inherently slower, less efficient, and more difficult to precisely control. When efforts have been made to externally preheat the mold, such as by a gas flame or torch, the gas flow creates significant noise problems and heating is grossly inefficient.
Still further, many of the prior approaches for casting straps lack adequate temperature control to insure that uniform fused bonds between the straps being formed and the plate lugs are achieved. This can create a situation in which some of the bonds may be satisfactory while other bonds are unsatisfactory. Should some of the bonds rupture in service, the electrical performance of the battery would, of course, be adversely affected.
As may be appreciated, the assembly of lead-acid batteries may require the transporting of molten lead or lead alloys for various purposes. One prior process has thus utilized pipe made of stainless steel and other metallic materials for transporting molten lead or lead alloys in a system where the material being transported is retained in the molten state by the resistance heating of the pipe. This approach has been used, for example, for transporting lead or lead alloys from a lead pot to a pouring ladle used to cast straps.
It is an object of the present invention to provide a method for more efficiently casting lug straps onto lead-acid battery cell elements.
Another object is to provide such a method and apparatus which ensures optimum casting conditions in the mold and molten lead at the time of casting.
A related and more specific object is to provide a method of the foregoing type which permits relatively precise control of the temperature of the mold and molten lead on a continuous basis, and which eliminates the necessity for critical timing in the casting operation following mold filling.
Yet another object of the present invention is to provide a method of the foregoing type in which relatively uniform fused bonds may be achieved.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which the present invention is utilized in the method and apparatus shown and described in the Schaumberg et al. application identified herein: